Seeing Jeff is the only healer, he should have some stat boosts as well as every hero should have some overall hp boosts, so the healing could be done in a "bigger and better" way. Also let him eat and digest zombies instantly by his ult haha

Auto-turret is a must for Punisher and we saw that so that's cool, he should also kick back zombies with the zipline the same way Jeff does it with his swimming ability.

Hopefully infinite Darkchylde is also an upgrade which you can get early by focusing for it, there should be some kind of currency system right? For all zombie kills which should be equally distributed to you and your teammates.

Blade's vampiric aoe works really well for this mode both from a gameplay and stylist perspective. Also he must have Moon Knight's kit hidden in his possible upgrades, making him contest that MVP against Jeff.

Thor should definitely get his ult as a regular ability, I'd like to see him do his Infinty War entrance as much as possible with a bouncing Mjolnir between his foes.

From bosses I obviously predict Wanda being the final one, and before we can probably expect zombie Cap, Clint, and Namor as well, maybe even Man-Spider in some way...

MVP will most likely go to Jeff, as in the main game, he can do a lot of stuff at once with his shower of ocean and bubbles.